Microelectromechanical microphone

ABSTRACT

A microelectromechanical microphone includes: a substrate; a sensor chip, integrating a microelectromechanical electroacoustic transducer; and a control chip operatively coupled to the sensor chip. In one embodiment, the sensor chip and the control chip are bonded to the substrate, and the sensor chip overlies, or at least partially overlies, the control chip. In another embodiment, the sensor is bonded to the substrate and a barrier is located around at least a portion of the sensor chip.

BACKGROUND Technical Field

The present disclosure relates to microelectromechanical microphones andto processes for manufacturing microelectromechanical microphones.

Description of the Related Art

Microelectromechanical microphones are known, which comprise a firstchip incorporating a microelectromechanical electroacoustic membranetransducer, and a second chip incorporating a control circuit or ASIC(Application-Specific Integrated Circuit). The electroacoustictransducer converts incident acoustic waves, which cause vibrations of amembrane, into electrical signals. For example, the membrane may becapacitively coupled to a reference electrode. The deformations of themembrane modify the capacitive coupling, which may be easily detectedwith a charge-amplifier circuit of the control circuit. The controlcircuit comprises signal-processing stages (for example, thecharge-amplifier circuit) and components suitable for interacting withand enabling operation of the microelectromechanical microphone, inparticular transduction of the acoustic signals.

The first chip and the second chip are housed within a same packagestructure for electronic devices, which generally includes a supportingsubstrate and a cap of plastic or metal material.

The substrate may be a polymeric or ceramic substrate, for example ofthe LGA (Land-Grid Array) type and is provided with connectionstructures (pads and lines) for electrical connection of the first chipand of the second chip, which are arranged alongside one another.Further, the substrate has an opening, also referred to as “sound port”,which enables transmission of the acoustic signals from outside of thepackage structure to the transducer that is inside the packagestructure.

The cap is bonded to the substrate and may have a dual function ofprotection and definition of an acoustic chamber and, for this reason,may have a determining effect upon the performance of themicroelectromechanical microphone.

The attention directed to the development and integration ofmicroelectromechanical sensors has been progressively increasing, instep with the spread of portable electronic devices such as smartphonesand tablets or other electronic devices of the so-called “wearable”type. The at times tumultuous development of products of this kind may,in some cases, set down specifications that are contrasting or difficultto reconcile. On the one hand, for example, there is the desire to offermicroelectromechanical transducers with increasingly higher levels ofperformance to meet the specifications of users. This generally leads toproviding chips of larger dimensions both for the microelectromechanicaltransducer and for the control circuit. On the other hand, instead,there is the contrasting desire to reduce more and more the dimensionsof microelectromechanical microphones, especially in portable andwearable systems.

Additionally, fitting two chips, such as a control ASIC and amicroelectromechanical transducers in the package can be difficult. Thesize of the chip incorporating the control ASIC is often reduced forallowing greater space for the chip incorporating the transducer.However, there is a desirable to increase the size of the chipincorporating the ASIC to make available a larger number of functionsfor control and processing of the transduced signals.

BRIEF SUMMARY

One or more embodiments of the present disclosure provide amicroelectromechanical microphone that may overcome or at leastattenuate one or more of the limitations described above.

Various aspects of the present disclosure are directed tomicroelectromechanical microphones and methods of making same inaccordance with various embodiments. For instance, in one embodiment isdirected to a microelectromechanical microphone comprising a substrate;a sensor chip bonded to the substrate and integrating amicroelectromechanical acoustic transducer; and a control chip bonded tothe substrate and operatively coupled to the sensor chip, the sensorchip having a first portion that is overlying and bonded to the controlchip.

In one embodiment the control chip has a first face, wherein the firstportion of the sensor chip is bonded to the first face of the controlchip, wherein the acoustic transducer includes a transduction memberacoustically communicating with a sound port in the substrate.

In one embodiment the substrate includes an assembly base, and thesensor chip has a second portion coupled to the base.

In one embodiment the microelectromechanical microphone comprises anadhesive layer that is partially on the base and partially on the firstface of the control chip along a perimeter of the sensor chip, thesensor chip being bonded to the base and to the control chip through theadhesive layer.

In one embodiment the base has a first thickness and the control chiphas a second thickness that is substantially the same thickness as thefirst thickness.

In one embodiment the base extends around the sound port.

In one embodiment the substrate includes a core of a rigid dielectricmaterial, and a metal layer on a face of the core, the sensor chip andthe control chip being bonded to the metal layer.

In one embodiment the control chip is fixed to the core of the substrateand has a face substantially flush with an assembly surface of the base.

In one embodiment the metal layer of the substrate defines a supportingportion; a solder mask is fixed to the supporting portion; and thesolder mask and the supporting portion of the metal layer form the base.

In one embodiment the microelectromechanical microphone comprises ahousing that houses the control chip, the housing being defined on oneside by the core of the substrate.

In one embodiment the housing is adjacent to the base.

In one embodiment the base is arranged adjacent to the sound port andhas a first thickness, the control chip having a second thickness thatis substantially equal to the first thickness.

In one embodiment the transduction member is centered around the soundport.

In one embodiment the transduction member comprises a membrane ofsemiconductor material extending over a cavity in a body of the sensorchip, the cavity being delimited on one side by the transduction memberand being open on an opposite side.

In one embodiment the cavity is acoustically coupled to the sound port.

In one embodiment the microelectromechanical microphone comprises a capbonded to the substrate and forming, with the cap, an acoustic chamberacoustically coupled with an environment outside of the microphonethrough the sound port, the acoustic chamber housing the control chipand the sensor chip.

Another embodiment is directed to an electronic system comprising acontrol unit and a microelectromechanical microphone operatively coupledto the control unit. The microelectromechanical microphone includes asubstrate having an inner surface and an outer surface; a control chipcoupled to the inner surface of the substrate; and a sensor chip havinga first surface portion coupled to the substrate and a second surfaceportion coupled to the control chip, the first and second surfaces beingcoplanar, the sensor chip integrating a microelectromechanical acoustictransducer.

The electronic system may be one of at least one of a cellphone, aportable computer, a video camera, a photographic camera, a multimediareader, a motion-activated user interface, a satellite-navigationdevice, and a wearable device.

The electronic system may further comprise a base coupled to thesubstrate and the sensor chip.

Another embodiment is directed to microelectromechanical microphonecomprising a package body including a first substrate and a cap coupledto the substrate and forming an inner cavity, the first substrate havingan inner surface and an outer surface and a through hole extending fromthe inner surface to outer surface. The microelectromechanicalmicrophone comprises a control chip in the inner cavity and coupled tothe inner surface of the substrate; a second substrate coupled to theinner surface of the substrate; and a sensor chip having a first portioncoupled directly to the second substrate and a second portion coupleddirectly to the control chip, the sensor chip including a membranefacing the through hole of the second substrate.

In one embodiment a surface of the second substrate and a surface of thecontrol chip are substantially coplanar, and wherein the first portionof the sensor chip is coupled to the surface of the second substrate andthe second portion of the sensor chip is coupled to the surface of thecontrol chip.

In one embodiment the second substrate is a C-shaped and located aroundthe through opening.

In one embodiment the second substrate is made of a material that is oneof a metal, glass, or silicon.

Various other aspects of the present disclosure are directed tomicroelectromechanical microphones and methods of making same inaccordance with other embodiments.

For instance, one embodiment is directed to a microelectromechanicalmicrophone comprising a supporting substrate having a first face and asecond face; a sensor chip bonded to the first face of the supportingsubstrate and integrating an microelectromechanical electroacoustictransducer; and a control chip having at least one portion between thefirst face and the second face of the supporting substrate andoperatively coupled to the sensor chip, the sensor chip being at leastpartially arranged on top of the control chip.

In one embodiment the supporting substrate has a through hole betweenthe first face and the second face, and the control chip is housed atleast partially in the through hole.

In one embodiment the microelectromechanical microphone comprises afixing structure laterally surrounding the control chip, wherein thecontrol chip is coupled to the supporting substrate by the fixingstructure.

In one embodiment the control chip has a face that is coplanar with thesecond face of the supporting substrate.

In one embodiment the control chip has a first thickness and thesupporting substrate has a second thickness, the second thickness beingsubstantially equal to first thickness.

In one embodiment the first thickness is greater than the secondthickness and the face of the control chip projects beyond the throughhole and the first face of the supporting substrate.

In one embodiment the control chip has a projecting portion and a recessthat receives a portion of the sensor chip.

In one embodiment the recess is delimited by a base that is coplanarwith the first face of the supporting substrate, wherein the recess isdelimited by a wall substantially perpendicular to the base, theprojecting portion of the control chip forming a step with respect tothe base of the recess.

In one embodiment a portion of the sensor chip has a recess that housesan edge of the control chip.

In one embodiment the control chip has a first thickness and thesupporting substrate has a second thickness, the first thickness beingsmaller than the second thickness, and wherein the fixing structure iscup-shaped.

In one embodiment a first face of the control chip is aligned with thefirst face of the supporting substrate, and a bottom portion of thefixing structure is aligned to the second face of the supportingsubstrate.

In one embodiment the substrate includes a mounting base, and the sensorchip has a first portion fixed to the control chip and a second portionfixed to the base.

In one embodiment the substrate includes a rigid dielectric material,and a metal layer on the rigid dielectric material, the sensor chip andthe control chip being fixed to the rigid dielectric material.

In one embodiment the metal layer defines a supporting portion; a soldermask is fixed to the supporting portion; and the solder mask and thesupporting portion of the metal layer form the base.

In one embodiment the supporting substrate is defined by the controlchip.

In one embodiment the microelectromechanical microphone comprises a capbonded to the supporting substrate, the cap forming, along with thesupporting substrate, an acoustic chamber, the sensor chip located inthe acoustic chamber and acoustically coupled with an externalenvironment through a sound port.

In one embodiment the sound port is in the supporting substrate.

In one embodiment the sound port is in the control chip.

In one embodiment a first portion of the sound port is defined in thesupporting substrate and a second portion of the sound port is definedin the control chip.

In one embodiment the sensor chip is centered around the sound port.

In one embodiment the sensor chip includes a transduction memberacoustically communicating with the outside through the sound port.

In one embodiment the transduction member includes a membrane ofsemiconductor material over a cavity in the sensor chip, the cavitybeing delimited on a first side by the transduction member andacoustically coupled to the sound port.

Another embodiment is directed to an electronic system comprising acontrol unit; and a microelectromechanical microphone operativelycoupled to the control unit. The microelectromechanical microphoneincludes a supporting substrate having a first face and a second face; asensor chip bonded to the first face of the supporting substrate andintegrating an microelectromechanical electroacoustic transducer; and acontrol chip having at least one portion between the first face and thesecond face of the supporting substrate and operatively coupled to thesensor chip, the sensor chip being at least partially arranged on top ofthe control chip.

The electronic system may be one of at least one of a cellphone, aportable computer, a video camera, a photographic camera, a multimediareader, a motion-activated user interface, a satellite-navigationdevice, and a wearable device.

Another embodiment is directed to a process for manufacturing amicroelectromechanical microphone comprising applying an adhesive-tapesupport to one of a first face and a second face of a supportingsubstrate, the adhesive-tape support covering a through hole thatextends through the supporting substrate from the first face to thesecond face; placing a control chip in the through opening; bonding thecontrol chip to the adhesive-tape support; and filling a space betweenwalls of the through hole and the control chip with a polymeric materialin a molding operation.

In one embodiment the process comprises bonding a sensor chip to thefirst face of the supporting substrate, the sensor chip including anelectroacoustic transducer.

In one embodiment the control chip has a first thickness and thesupporting substrate has a second thickness that is less than firstthickness, wherein the adhesive-tape support is applied to the secondface of the supporting substrate.

In one embodiment the control chip has a first thickness and thesupporting substrate has a second thickness that is less than the firstthickness, wherein the adhesive-tape support is applied to the firstface of the supporting substrate.

In one embodiment the process comprises removing the adhesive-tapesupport after filling the space.

Various other aspects of the present disclosure are directed tomicroelectromechanical microphones and methods of making same inaccordance with yet other embodiments.

For instance, one embodiment is directed to a microelectromechanicalmicrophone comprising a substrate having an inner surface and an outersurface; a sensor chip having a first face and second face, the firstface of the senor chip coupled to the inner surface of substrate, thesecond face of the sensor chip integrating a MEMS electroacoustictransducer; a control chip coupled to the substrate and operativelycoupled to the sensor chip; a bonding ring surrounding the sensor chipand the control chip; a cap coupled to the substrate by the bonding ringand forming an acoustic chamber with the substrate, the control chip andthe sensor chip located in the acoustic chamber; and a barrier betweenthe bonding ring and the sensor chip, the barrier being located a firstdistance from the bonding ring and defining a first trench, the barrierbeing located a second distance from the sensor chip and defining asecond trench.

In one embodiment the sensor chip is shaped to have one or more roundedcorners or chamfered corners.

In one embodiment the corners are chamfered on one side of the sensorchip, the side of the sensor chip that is chamfered includes the secondface of the sensor chip.

In one embodiment at the one or more rounded corners the barrier formscurvilinear paths having a first radius of curvature, and wherein theone or more rounded corners have a second radius of curvature equal tothe first radius of curvature.

In one embodiment the sensor chip has side walls extending between thefirst face and the second face, the sensor chip being coupled to thesubstrate at the second face and having a perimetral recess that extendsalong bottom portions of the side walls so that the area of the firstface is 10%-25% greater than the area of the second face.

In one embodiment the perimetral recess extends, starting from thesecond face, towards the first face up to a height that is greater thana height of the barrier.

In one embodiment the microelectromechanical microphone comprises a gluelayer, wherein the sensor chip is coupled to the substrate by the gluelayer, the second trench forming a region of accumulation for excessglue that flows out of the glue layer.

In one embodiment the microelectromechanical microphone comprises asolder paste layer wherein the cap is coupled to the bonding ring by thesolder paste layer, the first trench forming a region of accumulationfor excess solder paste that flows out of the solder-paste layer.

In one embodiment the barrier has a height that is between 15 μm and 25μm.

In one embodiment the sensor chip includes a transduction member inacoustic communication with a sound port in the substrate.

In one embodiment the substrate includes a dielectric material and ametal layer on a face of the dielectric material, the sensor chip andthe control chip being coupled to the dielectric material, and the firstand second trenches extending in the metal layer.

In one embodiment the microelectromechanical microphone comprises asolder mask, wherein the control chip is fixed to the dielectricmaterial of the substrate by the solder mask.

Another embodiment is directed to an electronic system comprising acontrol unit; and a microelectromechanical microphone operativelycoupled to the control unit. The microelectromechanical microphoneincludes a substrate having an inner surface and an outer surface; asensor chip having a first face and second face, the first face of thesenor chip coupled to the inner surface of substrate, the second face ofthe sensor chip integrating a MEMS electroacoustic transducer; a controlchip coupled to the substrate and operatively coupled to the sensorchip; a bonding ring surrounding the sensor chip and the control chip; acap coupled to the substrate by the bonding ring and forming an acousticchamber with the substrate, the control chip and the sensor chip locatedin the acoustic chamber; and a barrier between the bonding ring and thesensor chip, the barrier being located a first distance from the bondingring and defining a first trench, the barrier being located a seconddistance from the sensor chip and defining a second trench.

The electronic system may be one of at least one of a cellphone, aportable computer, a video camera, a photographic camera, a multimediareader, a motion-activated user interface, a satellite-navigationdevice, and a wearable device.

Another embodiment is directed to a process for manufacturing amicroelectromechanical microphone. The process includes bonding a sensorchip integrating a microelectromechanical electroacoustic transducer toa first surface of a substrate; mechanically coupling a control chip tothe first surface of the substrate and operatively coupling the controlchip to the sensor chip; forming a barrier on the first surface of thesubstrate; coupling a cap to the substrate by a bonding ring around thesensor chip and the control chip, the cap and the substrate forming anacoustic chamber, the control chip and the sensor chip being located inthe acoustic chamber; and wherein the barrier is between the bondingring and the sensor chip, the barrier being at a first distance from thebonding ring to form a first trench and at a second distance from thesensor chip to form a second.

In one embodiment the sensor chip has a polygonal shape with sharpcorners.

In one embodiment the process comprises shaping at least one of thesharp corners by forming rounded corners or chamfered corners.

In one embodiment the sensor chip has a first face, a second face, andside walls that extend between the first face and the second face, thesensor chip being coupled to the substrate by the first face, theprocess further comprising removing portions of the side walls of thesensor chip and including the side walls at the first face but notincluding the side walls at the second face to form a perimetral recesssuch that the area of the second face is 10%-25% greater than the areaof the first face.

In one embodiment the area of the second face is 15% greater than thearea of the first face.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a better understanding of the disclosure, some embodiments thereofwill now be described, purely by way of non-limiting example and withreference to the attached drawings, in which:

FIG. 1 is a top plan view, partially sectioned along a longitudinalplane, of a microelectromechanical microphone according to oneembodiment of the present disclosure;

FIG. 2 is a plan view from beneath of the microelectromechanicalmicrophone of FIG. 1;

FIG. 3 is a side view of the microelectromechanical microphone of FIG.1, sectioned along the line III-III of FIG. 1;

FIG. 4 is a perspective view of the microelectromechanical microphone ofFIG. 1, sectioned along the line III-III of FIG. 1 and with partsremoved for clarity;

FIGS. 5-8 are perspective views of the microelectromechanical microphoneof FIG. 1 during an assembly procedure;

FIG. 9 is a top plan view, partially sectioned along a longitudinalplane, of a microelectromechanical microphone according to a differentembodiment of the present disclosure;

FIG. 10 is a plan view from beneath of the microelectromechanicalmicrophone of FIG. 9;

FIG. 11 is a perspective view of the microelectromechanical microphoneof FIG. 5, partially sectioned along the line XI-XI of FIG. 9 and withparts removed for clarity;

FIG. 12 is a partially sectioned top plan view of amicroelectromechanical microphone according to another embodiment;

FIG. 13 is a plan view from beneath of the microelectromechanicalmicrophone of FIG. 12;

FIG. 14 is a side view of the microelectromechanical microphone of FIG.12, sectioned along the line III-III of FIG. 12;

FIG. 15 is a perspective view of the microelectromechanical microphoneof FIG. 12, sectioned along the line III-III of FIG. 12 and with partsremoved for clarity;

FIG. 16 is a cross-sectional view of the microelectromechanicalmicrophone of FIG. 12 in a first step of a manufacturing process,according to an embodiment;

FIG. 17 shows the view of FIG. 16 in a second step of the manufacturingprocess;

FIG. 18 is a cross-sectional view through a microelectromechanicalmicrophone according to a different embodiment;

FIG. 19 is a cross-section of the microelectromechanical microphone ofFIG. 18 in a first step of a manufacturing process, according to afurther embodiment;

FIG. 20 shows the view of FIG. 19 in a second step of the manufacturingprocess;

FIG. 21 is a cross-sectional view through a microelectromechanicalmicrophone according to a different embodiment;

FIG. 22 is a cross-sectional view through a microelectromechanicalmicrophone according to a different embodiment;

FIG. 23 is a cross-sectional view through a microelectromechanicalmicrophone according to a different embodiment;

FIG. 24 is a cross-sectional view through a microelectromechanicalmicrophone according to a different embodiment;

FIG. 25 is a top plan view, partially sectioned and with parts removedfor clarity, of a microelectromechanical microphone according to afurther embodiment;

FIG. 26 is a cross-sectional view through a microelectromechanicalmicrophone according to a different embodiment;

FIG. 27 is a cross-sectional view through a microelectromechanicalmicrophone according to a different embodiment;

FIG. 28 is a top plan view, partially sectioned along a longitudinalplane, of a microelectromechanical microphone according to anotherembodiment;

FIG. 29 is a lateral sectional view of the microelectromechanicalmicrophone of FIG. 28, sectioned along the line II-II of FIG. 28;

FIG. 30 is a perspective view of the microelectromechanical microphoneof FIGS. 28 and 29;

FIGS. 31-34 are respective perspective views of microelectromechanicalmicrophones according to further embodiments;

FIG. 35 is a lateral sectional view of the micro-electro-mechanicalmicrophone of FIG. 34; and

FIG. 36 is a simplified block diagram of an electronic system thatincorporates a microelectromechanical microphone according to oneembodiment of the present disclosure.

DETAILED DESCRIPTION

Features described herein that have same reference numbers have the samestructure and function and thus may not be described again in theinterest of brevity.

With reference to FIGS. 1 to 4, a microelectromechanical microphoneaccording to one embodiment of the present disclosure is designated as awhole by the reference number 1 and comprises a substrate 2, a cap 3, asensor chip 5, and a control chip 6. The sensor chip 5 and the controlchip 6 are operatively coupled together.

The substrate 2 and the cap 3 are bonded together (FIG. 3) and form apackage structure, inside which the sensor chip 5 and the control chip 6are housed. The cap 3 has a protective function and also defines anacoustic chamber 4 of the microelectromechanical microphone 1.

In one embodiment, the substrate 2 may be a substrate of an LGA type andcomprises: a core 7; an external metal layer 8 and an internal metallayer 9, for example of copper, on opposite faces of the core 7; and asolder mask 10. A through hole in the substrate 2 defines a sound port11 and enables acoustic coupling of the inside of the package structure,in particular of the sensor chip 5, with the external environment.

The core 7 (FIGS. 3 and 4) is defined by a chip of rigid dielectricmaterial, for example FR4, having a major, longitudinal, dimension and aminor, transverse, dimension.

The external metal layer 8 (FIG. 2) is arranged on an outer face of thecore 7, i.e., opposite to the cap 3. Defined in the external metal layer8 are first features, amongst which, in particular, external contacts 12for electrical connection of the microelectromechanical microphone 1 andan external guard ring 13 around the sound port 11. The external guardring 13 may be used also for connection to ground and is thus alsoreferred to as a “ground ring”.

The internal metal layer 9 (FIGS. 1, 3, and 4) is arranged on an innerface of the core 7, closed by the cap 3. Defined in the internal metallayer 9 are second features, amongst which internal contacts 15, abonding ring 16, along the perimeter of the core 7, an internal guardring 17 around the sound port 11, and a supporting portion 18.

The cap 3 is fixed to the bonding ring 16.

The internal contacts 15 are electrically coupled to respective externalcontacts 12 with through vias 20 in the core 7. In one embodiment, theinternal contacts 15 are aligned and are arranged at one end of thesubstrate 2 longitudinally opposite with respect to the sound port 11.

The solder mask 10 is bonded to the supporting portion 18 of theinternal metal layer 9. In one embodiment, the solder mask 10 and thesupporting portion 18 are shaped so as to present, in plan view, a sameprofile and together define a contact island 21, around the internalcontacts 15, an assembly base 22 around the sound port 11, and a housing24 between the base 22 and the contact island 21.

The contact island 21 surrounds the internal contacts 15, separatingthem laterally from the rest of the conductive structures on thesubstrate 2.

The base 22 functions as anchorage for the sensor chip 5. For thispurpose, the base 22 extends over an area sufficient for supporting thesensor chip 5 in a stable way astride of the sound port 11. In oneembodiment, the base 22 is substantially C-shaped and extends around thesound port 11 along three sides of the substrate 2.

The housing 24 is defined by a recess delimited on one side by the base22 and on an opposite side by the contact island 21. The housing 24 mayfurther be delimited on the sides by perimetral walls 25, which join thecontact island 21 to the base 22. On the bottom, the housing 24 isdelimited by the core 7. The depth of the housing 24 is substantiallyequal to the height of the internal metal layer 9 and of the solder mask10.

The control chip 6 houses an integrated control circuit or ASIC (notshown in detail), which comprises signal-processing stages (for example,a charge-amplifier circuit for a capacitive electroacoustic sensor) andthe components suitable for interacting with and enabling operation ofthe microphone, in particular as regards to transduction of the acousticsignals. The control chip 6 is arranged within the housing 24, withoutobstructing the sound port 11. In greater detail, a face of the controlchip 6 is bonded to the core 7 of the substrate 2 by an adhesive layer26. The adhesive layer 26 may, for example, be a layer of glue dispensedon the core 7 of the substrate 2 within the housing 24 or else anadhesive tape. On an opposite face, the control chip 6 has contact pads28 for connection to the internal contacts 15 by first wire bondings 30and to the sensor chip 5 by second wire bondings 31.

The control chip 6 and the adhesive layer 26 have an overall thicknesssubstantially equal to the depth of the housing 24 in such a way thatthe control chip 6 does not project in a significant way with respect tothe height of the solder mask 10. Possibly, the control chip 6 mayundergo mechanical or chemical-mechanical surface machining, such aschemical mechanical polishing (CMP), in order to adapt the thickness tothe depth of the housing 24. A face 6 a of the control chip 6 is thussubstantially flush with an assembly surface 22 a of the base 22, i.e.,in practice, with the surface of the solder mask 10 opposite to theinternal metal layer 9. However, also the case where the face 6 a of thecontrol chip 6 is arranged in or projects slightly may be toleratedwithout specifying for particular arrangements in order to compensatefor the misalignment.

An electroacoustic transducer 35 is integrated in the sensor chip 5 and,in one embodiment, comprises a membrane 37 of semiconductor material,extending over a cavity 38 formed in the body 5 a of the sensor chip 5,and a rigid metal backplate 40, capacitively coupled to the membrane 37.The backplate 40 is provided with holes and is arranged alongside themembrane 37 on the side opposite to the cavity 38. The cavity 38 isdelimited on one side by the membrane 37 and is open on the oppositeside.

The sensor chip 5 is bonded to the substrate 2 in such a way that themembrane 37 is in acoustic communication with the outside of the packagestructure formed by the substrate 2 and by the cap 3 through the soundport 11. In one embodiment, the sensor chip 5 is centered around thesound port 11.

Further, the sensor chip 5 is in part arranged longitudinally on top ofthe control chip 6, which, as already mentioned, is substantially flushwith the solder mask 10. In greater detail, the sensor chip 5 has afirst portion fixed to the face 6 a of the control chip 6 and a secondportion fixed to the base 22 around the sound port 11. Fixing isobtained by an adhesive layer 41, for example a glue or a solderingpaste, which extends in part on the base 22 and in part on the face 6 aof the control chip 6, along the perimeter of the sensor chip 5.

Given the same dimensions, setting the sensor chip 5 and the controlchip 6 on top of one another, with the control chip 6 located in thehousing 24 and the sensor chip 5 fixed in part to the base 22, enablesreduction of the overall area occupied, without increasing the totalthickness of the microelectromechanical microphone 1. Vice versa, giventhe same area occupied, the sensor chip 5 and the control chip 6 mayhave larger dimensions, to the advantage of performance.

Assembly of the microelectromechanical microphone 1 may be carried outin the way described in what follows with reference to FIGS. 5 to 8.Initially, the external metal layer 8, the internal metal layer 9, andthe solder mask 10 are defined with photolithographic processes toobtain the external contacts 12, the internal contacts 15, the bondingring 16, and the base 22 (FIG. 5) using standard techniques. Theadhesive layer 26 is dispensed or arranged (according to the type ofadhesive used) on the bottom of the housing 24 (FIG. 6). The controlchip 6 is bonded to the substrate 2 by the adhesive layer 26 (FIG. 7).The adhesive layer 41 is laid on the base 22 and on part of the face 6 aof the control chip 6, and the sensor chip 5 is bonded to the substrate2 and to the control chip 6 by the adhesive layer 41 (FIG. 8). The wirebondings 30 are formed between the control chip 6 and the internalelectrodes 15, the wire bondings 31 are formed between the control chip6 and the sensor chip 5, and the cap 3 is bonded to the bonding ring 16of the substrate 2, thus obtaining the structure of FIG. 1.

A different embodiment of the disclosure is illustrated in FIGS. 9 to11. In this case, a microelectromechanical microphone 100 comprises asubstrate 102, a cap 103, a sensor chip 105, and a control chip 106.

The sensor chip 105 and the control chip 106 are operatively coupledtogether and are housed within a package structure defined by thesubstrate 102 and by the cap 103 bonded together.

The substrate 102 comprises a core 107, an external metal layer 108, andan internal metal layer 109. A through hole in the substrate 102 definesa sound port 111.

The external metal layer 108 (FIG. 10) forms external contacts 112 andan external guard ring 113 around the sound port 111.

The internal metal layer 109 (FIGS. 9 and 11), on a face of the core 107opposite to the external metal layer 108, defines internal contacts 115,a bonding ring 116 for the cap 103, and an internal guard ring 117around the sound port 111. A solder mask 110 defines, with a portion ofthe internal metal layer 109, a contact island 121 around the externalcontacts.

An assembly base 122 is defined around the sound port 111 on the face ofthe core 107 on which the internal metal layer 109 is located. The base122 is C-shaped and extends around the sound port 111, withoutobstructing it.

The base 122 may, for example, be of metal, glass, or silicon and has athickness substantially equal to the thickness of the control chip 106.

The control chip 106, which comprises signal-processing stages andcomponents suitable for interacting with and enabling operation of themicroelectromechanical microphone 100, is bonded to the core 107 of thesubstrate 102 by an adhesive layer 126 and is arranged adjacent to thebase 122, without obstructing the sound port 111.

The sensor chip 105 integrates an electroacoustic transducer 135 (FIG.11) substantially of the type already described with reference to FIGS.1 to 4. In particular, the electroacoustic transducer 135 comprises amembrane 137, extending over a cavity 138, and a rigid metal backplate140, capacitively coupled to the membrane 137 on the side opposite tothe cavity 138. The cavity 138 is delimited on one side by the membrane137 and is open on the opposite side.

The sensor chip 105 is bonded to the substrate 102 so as to be inacoustic communication with the outside of the package structure formedby the substrate 102 and the cap 103 through the sound port 111. In oneembodiment, the sensor chip 105 is centered around the sound port 111.

In addition, the sensor chip 105 is longitudinally arranged in part onthe control chip 106, which is substantially flush with an assemblysurface 122 a of the base 122. In greater detail, the sensor chip 105has a first portion fixed to a face 106 a of the control chip 106 and asecond portion fixed to the base 122 around the sound port 111. Fixingis obtained by an adhesive layer 141, for example a glue or a solderingpaste, which extends along the perimeter of the sensor chip 105.

The cap 103 is bonded to the substrate 102 along the bonding ring 116.

In this case, there are no constraints on the thickness of the controlchip 106, since the base 122 may have an arbitrary thickness. Alignmentbetween the face 106 a of the control chip 106 and the base 122 to havea uniform bonding surface may be obtained by controlling the thicknessof the base 122 during manufacture.

With reference to FIGS. 12-15, a microelectromechanical microphoneaccording to another embodiment designated as a whole by the number 1 awill now be described. The microelectromechanical microphone isdifferent from the microelectromechanical microphone 1 in that controlchip 6 is located in an opening of the through core 7 as well as otherfeatures that will be described in detail below.

The microelectromechanical microphone 1 a includes a supportingsubstrate 2, a cap 3, a sensor chip 5, and a control chip 6. The sensorchip 5 and the control chip 6 are operatively coupled together.

The substrate 2 and the cap 3 are bonded together (FIG. 12) and form apackage, which houses the sensor chip 5 and the control chip 6. The cap3 has a protective function and further defines an acoustic chamber 4 ofthe microelectromechanical microphone 1.

In an embodiment, the substrate 2 may be a substrate of an LGA(Land-Grid Array) type and comprises a core 7, an outer metal layer 8and an inner metal layer 9, for example made of copper and arranged onopposite faces of the core 7, and a solder mask 10. A through hole inthe substrate 2 defines a sound port 11 and enables acoustic coupling ofthe inside of the package, in particular of the sensor chip 5, with theexternal environment.

A further through hole in the substrate 2 defines a through hole 34 inwhich the control chip 6 is at least partially housed.

The core 7 (FIGS. 14 and 15) is defined by a plate of rigid dielectricmaterial, for example FR4, having a larger longitudinal dimension and asmaller transverse dimension.

The outer metal layer 8 (FIG. 13) is arranged on an outer face of thecore 7, i.e., opposite to the cap 3. Defined in the outer metal layer 8are first features, amongst which, in particular, external contacts 14for electrical connection of the microelectromechanical microphone 1,and an outer guard ring 13 around the sound port 11. The outer guardring 13 may be used also for connection to ground and is hence alsoreferred to as “ground ring”. A further solder mask 19 may be applied tothe outer metal layer 8.

The inner metal layer 9 (FIGS. 12, 14, and 15) is arranged on an innerface of the core 7, closed by the cap 3. Defined in the inner metallayer 9 are second features, amongst which internal contacts 15, abonding ring 16, along the perimeter of the core 7, an inner guard ring17 around the sound port 11, and a supporting portion 18.

The cap 3 is fixed to the bonding ring 16. The internal contacts 15 areelectrically coupled to respective external contacts 14 by through vias20 in the core 7. In one embodiment, the internal contacts 15 arealigned and are arranged at one end of the substrate 2 longitudinallyopposite with respect to the sound port 11.

The solder mask 10 adheres to the supporting portion 18 of the innermetal layer 9. In one embodiment, the solder mask 10 and the supportingportion 18 are shaped for having, in plan view, a same profile andtogether define a contact island 21 around the internal contacts 15, anda mounting base 22 around the sound port 11. The contact island 21 andthe base 22 are located at opposite sides of the through hole 34. Thebase 22 is adjacent to the hole 34.

The contact island 21 surrounds the internal contacts 15, separatingthem laterally from the rest of the conductive structures on thesubstrate 2.

The base 22 functions as anchorage for the sensor chip 5. For thispurpose, the base 22 extends over an area sufficient to support thesensor chip 5 in a stable way straddling the sound port 11. In oneembodiment, the base 22 extends around the sound port 11.

The control chip 6 houses an integrated control circuit or ASIC(Application-Specific Integrated Circuit), not illustrated in detail,which comprises signal-processing stages (for example, acharge-amplifier circuit for a capacitive electroacoustic sensor) andthe components for interacting with and enabling operation of themicrophone, in particular with regards to transduction of the acousticsignals.

The control chip 6 is housed in the through hole 34. In greater detail,in one embodiment the control chip 6 has a smaller length and width thanthe length and width of the through hole 34, so that the control chip 6will not be directly in contact with at least one of the walls thatdelimit the through hole 34. Furthermore, the control chip 6 has athickness substantially equal to the thickness of the substrate 2 and iscontained in a region delimited by an inner face 2 a and by an outerface 2 b of the substrate 2. In other words, the control chip 6 has aninner face 6 a aligned to the inner face 2 a of the substrate 2 and anouter face 6 b aligned to the outer face of the substrate 2. In oneembodiment (not shown), in which there are no solder masks on the twofaces of the substrate 2, the control chip 6 has the inner face 6 a andthe outer face 6 b aligned, respectively, to an outer face and to aninner face of the core 7 of the substrate 2. Possibly, the control chip6 may undergo machining or a chemico-mechanical surface treatment inorder to adapt the thickness to the depth of the through hole 34. Alsothe case where the face 6 a of the control chip 6 is recessed orprojects slightly may be tolerated without need for particular measuresfor offsetting any misalignment.

The control chip 6 is connected to the substrate 2 and held within thethrough hole 34 by a fixing frame 32, which occupies the space betweenthe control chip 6 and the walls that delimit the through hole 34. Thefixing frame 32 may, for example, be made by molding of polymericmaterial, as explained hereinafter. To favour production of the fixingframe 32 using molding techniques, the solder mask 10, and acorresponding portion of the inner metal layer 9 may extend along thesides of the through hole 34 between the contact island 21 and the base22.

On the inner face 6 a, the control chip 6 has contact pads 28 forcoupling to the internal contacts 15 through first wire bondings 30 andto the sensor chip 5 through second wire bondings 31.

An electroacoustic transducer 35 (FIGS. 14 and 15) is integrated in thesensor chip 5 and, in one embodiment, comprises a membrane 37 ofsemiconductor material, stretched over a cavity 38 formed in the body 5a of the sensor chip 5, and a rigid metal backplate 40, capacitivelycoupled to the membrane 37. The backplate 40 is provided with holes andis arranged alongside the membrane 37 on the side opposite to the cavity38. The cavity 38 is delimited on one side by the membrane 37 and isopen on the opposite side.

The sensor chip 5 is bonded to the substrate 2 so that the membrane 37is in acoustic communication with the outside of the package formed bythe substrate 2 and by the cap 3 through the sound port 11. In oneembodiment, the sensor chip 5 is centred around the sound port 11.

Furthermore, the sensor chip 5 is partially arranged on top of thecontrol chip 6, which, as already mentioned, is substantially aligned tothe solder mask 10. In greater detail, the sensor chip 5 has a firstportion fixed to the face 6 a of the control chip 6 and a second portionfixed to the base 22 around the sound port 11. Fixing is obtained by anadhesive layer 41, for example a glue or a solder paste, which extendsin part over the base 22 and in part over the face 6 a of the controlchip 6, along the perimeter of the sensor chip 5.

Given the same dimensions, the superposition of the sensor chip 5 and ofthe control chip 6, with the control chip 6 arranged in the through hole34 and the sensor chip 5 partially fixed to the base 22, enablesreduction of the total area occupied, without increasing the totalthickness of the microelectromechanical microphone 1. Conversely, giventhe same area occupied, the sensor chip 5 and the control chip 6 mayhave larger dimensions, to the advantage of performance. Furthermore,given that the through hole 34 for housing the control chip 6 extendsbasically throughout the thickness of the substrate 2, the dimensions ofthe control chip 6 may be adapted to the through hole 34 with a minimalthinning, if so desired. In other cases, the control chip 6 may behoused without any type of preliminary thinning process.

The microelectromechanical microphone 1 may be obtained as described inwhat follows, with reference to FIGS. 16 and 17.

Initially, the substrate 2 is prepared. Preparation of the substrate 2includes definition of the outer metal layer 8, of the inner metal layer9, of the solder mask 10, and of the solder mask 19 for providing thefeatures on the faces of the substrate 2, amongst which, in particular,the contact island 21, the base 22, the outer guard ring 13, the innerguard ring 17, the bonding ring 16 and the contacts 14, 15. Preparationfurther includes drilling of the substrate 2 for providing the soundport 11 and the through hole 34 for housing the control chip 6.

An adhesive-tape support 43 is applied to a face of the substrate 2, forexample the outer face 2 b, as illustrated in FIG. 16. The adhesive-tapesupport 43 may cover the entire outer face 2 b of the substrate 2 and inany case closes the through hole 34 on one side.

By a pick-and-place operation, the control chip 6 is then introducedinto the through hole 34 from the open side of the latter and is bondedto the adhesive-tape support 43. The adhesive-tape support 43 holds thecontrol chip 6 within the through hole 34. The space between the wall ofthe through hole 34 and the control chip 6 (in practice a frame that hasa thickness substantially equal to the thickness of the substrate 2 anda shape corresponding to that of the fixing frame 32) defines a mold 32a that is filled with polymeric material by a molding operation, forexample according to a technique of film-assisted molding. The fixingframe 32 is thus formed, as illustrated in FIG. 17.

After the adhesive-tape support 43 has been removed, themicroelectromechanical microphone 1 is completed by bonding the sensorchip 5 to the substrate 2 and, in part, to the control chip 6, to obtainthe wire bondings 30, 31 and by bonding the cap 3 to the substrate 2along the bonding ring 16.

In a different embodiment of the disclosure (illustrated in FIG. 18),the control chip, here designated by 106, has a thickness smaller thanthat of the substrate 2, in particular a thickness smaller than that ofthe core 7 of the substrate 2. The control chip 106 is housed in thethrough hole 34, with an inner face 106 a aligned to the inner face 2 aof the substrate 2, and is connected to the substrate 2 by a fixingstructure 125. The fixing structure 125 is cup-shaped and also covers anouter face 106 b of the control chip 106, in addition to its lateralsurfaces. The bottom of the fixing structure 125 is aligned to the outerface 2 b of the substrate 2.

Also in this case, a microelectromechanical microphone 100 may beproduced with the aid of an adhesive-tape support.

With reference to FIG. 19, after preparation of the substrate 2, anadhesive-tape support 143 is applied to the inner face 2 a of thesubstrate 2. By a pick-and-place operation, the control chip 6 isarranged in the through hole 12 and held therein by the adhesive-tapesupport 143.

The fixing structure 125 is then provided by molding, for example usingthe pin-gate-molding technique (FIG. 20), and the adhesive-tape support143 is removed.

Finally, the sensor chip 5 is bonded to the substrate 2 and in part tothe control chip 6, the wire bondings 30, 31 are provided, and the cap 3is bonded to the substrate 2 along the bonding ring 16.

According to one embodiment, illustrated in FIG. 21, in amicroelectromechanical microphone 200 the control chip, here designatedby 206, may have a thickness greater than that of the substrate 2. Inthis case, the control chip 206 is housed only partially in the throughhole 12 and is connected to the substrate 2 by a fixing frame 225 ofpolymeric material, for example obtained by molding. In particular, thecontrol chip 206 has an outer face 206 a aligned to the outer face 2 bof the substrate 2 and projects from the through hole 12 towards theinside of the acoustic chamber 4. In greater detail, the control chip206 has a projecting portion 206 c and a recess 250 that accommodatespart of the sensor chip 5. The recess 250 is obtained by etching thecontrol chip 206 and is delimited by a base, aligned to the inner face 2a of the substrate 2, and by a wall substantially perpendicular to thebase. In practice, the projecting portion 206 c of the control chipforms a step with respect to the base of the recess 250. An edge of thesensor chip 5 adjacent to the control chip 206 is housed in the recess250 and may be bonded to the portion of the control chip 206 thatdefines the base of the recess 250.

The microelectromechanical microphone 200 may be assembled following theprocess described in FIGS. 16 and 17.

According to the embodiment illustrated in FIG. 22, in amicroelectromechanical microphone 300 the control chip, here designatedby 306, is partially housed in the through hole 12 and, since it has athickness greater than that of the substrate 2, projects towards theinside of the acoustic chamber 4. In a portion of the sensor chip 305adjacent to the control chip 306, a recess 350 is provided that housesan edge of the control chip 306 itself. The recess 350 is obtained byetching the sensor chip 305 at its base, in a position adjacent to thecontrol chip 306, and is delimited by two walls that are parallel one toa side face and the other to the inner face 306 a of the control chip306. A part of the sensor chip 305 is arranged on top of the controlchip 306 and may be bonded thereto.

Also in this case, the control chip 306 is connected to the substrate 2by a fixing frame 325 of polymeric material, which is obtained bymolding and occupies the space between the control chip 306 and the wallthat delimits the through hole 12. Furthermore, an outer face 306 b ofthe control chip 306 is aligned to the outer face 2 b of the substrate2.

FIG. 23 illustrates an embodiment of the disclosure in which thesubstrate and the control chip, here designated, respectively, by 402and 406, are connected together by a fixing frame 425 of polymericmaterial and are both provided with contacts 450 of a BGA (Ball-GridArray) type. In this case, part of the electrical connections betweenthe inner face 406 a and the outer face 406 b of the control chip 406are obtained by TSVs (Through Silicon Vias) 451 provided in the controlchip 406 itself. Wire bondings are used for connecting the sensor chip 5to the control chip 406. Connection paths (not illustrated) may beprovided, as desired, directly on a face of the control chip 406.

In one embodiment (not shown), the connections from inside the acousticchamber 4 to the outside may be obtained in part as through vias in thecontrol chip 406 and in part as wire bondings and through vias in thesubstrate 402.

According to the embodiment illustrated in FIG. 24, the control chip,here designated by 506, is housed in a through hole 512 of the substrate502, in this case without projecting beyond the inner face 502 a and theouter face 502 b of the substrate 502. The control chip 506 is connectedto the substrate 502 by a fixing frame 525 of polymeric material.

The sensor chip 505 is bonded partly to an inner face 502 a of thesubstrate 502 and partly to an inner face 506 a of the control chip 506,which are aligned to one another.

A sound port 511 is defined by a through hole in the control chip 506and enables acoustic coupling of the inside of the package formed by thecap 3, the substrate 502, and the control chip 506 with the externalenvironment.

According to the embodiment of FIG. 25, the substrate and the controlchip, which are designated by 602 and 606, respectively, each define acorresponding portion of sound port 611. In other words, the sound port611 is obtained by removal of a portion of the substrate 602 and aportion of the control chip 606 and is defined when the control chip 606is housed in its through hole 612 within the substrate 602. The controlchip 606 is housed in a through hole 612 and connected to the substrate602 by a fixing frame 625.

The embodiment illustrated in FIG. 26 differs from the embodiment ofFIGS. 12-15 in that the sound port, here designated by 711, is providedin the cap 703. In this case, then, the substrate 702 is continuous inthe region corresponding to the sensor chip 5.

With reference to FIG. 27, according to an embodiment of the disclosure,a microelectromechanical microphone 800 comprises a cap 803, a sensorchip 805, and a control chip 806.

The control chip 806, which functions as supporting substrate, and thecap 803 are bonded together along the perimeter of the cap 803 and forma package, which houses the sensor chip 805. The cap 803 has aprotective function and, further, defines with the control chip 806 anacoustic chamber 804 of the microelectromechanical microphone 800.

The control chip 806 is, for example, of the BGA type and houses anintegrated control circuit (not shown in detail), which comprisessignal-processing stages (for example, a charge-amplifier circuit for acapacitive electroacoustic sensor) and the components useful forinteracting with and enabling operation of the microphone, in particularin regards to transduction of the acoustic signals.

The control chip 806 has a through hole that defines a sound port 811and enables acoustic coupling of the inside of the package, inparticular of the sensor chip 805, with the external environment.

An electroacoustic transducer 835 is integrated in the sensor chip 805and, in one embodiment, comprises a membrane 837 of semiconductormaterial, stretched over a cavity 838 formed in the body 805 a of thesensor chip 805, and a rigid metal backplate 840, capacitively coupledto the membrane 837. The backplate 840 is provided with holes and isarranged alongside the membrane 837 on the side opposite to the cavity838. The cavity 838 is delimited on one side by the membrane 837 and isopen on the opposite side.

The sensor chip 805 is bonded to an inner face 806 a of the control chip806 so that the membrane 837 is in acoustic communication with theoutside of the package formed by the control chip 806 and by the cap 803through the sound port 811. Fixing is obtained by an adhesive layer 841that extends over the face 806 a of the control chip 806 around thesound port 811.

It is to be appreciated that the various embodiments enable saving of asubstrate otherwise used substantially for mechanical support and forproviding electrical connections, but without an active role in theprocess of transduction of the acoustic signals.

With reference to FIGS. 28-30, a microelectromechanical microphone 1 bis provided according to one embodiment of the present disclosure. FIG.28 shows a top plan view of the microelectromechanical microphone 1 b,in a plane XY. FIG. 29 shows a lateral sectional view of themicroelectromechanical microphone 1, in a plane XZ. FIG. 30 shows aperspective view of the microelectromechanical microphone 1 b, in atriaxial system XYZ.

The microelectromechanical microphone is different from themicroelectromechanical microphones 1 and 1 a in that control chip 6 islocated on xx 10, as well as other features that will be described indetail below.

The microelectromechanical microphone 1 b comprises a substrate 2, a cap3, a sensor chip 5, and a control chip 6. The sensor chip 5 and thecontrol chip 6 are operatively (e.g., electrically) coupled together,for example by bonding wires 31.

It is here pointed out that, for simplicity of representation, FIG. 30illustrates the microelectromechanical microphone 1 b without the cap 3,so that the internal structure of the microelectromechanical microphone1 b and the mutual arrangement of the elements that form themicroelectromechanical microphone 1 b itself are appreciated morereadily.

The substrate 2 and the cap 3 are coupled together by a solder-pasteregion 22 and form a package structure defining an internal cavity 4, inwhich the sensor chip 5 and the control chip 6 are housed. The cap 3 hasa protective function. The internal cavity 4 forms an acoustic chamberof the microelectromechanical microphone 1 b.

In one embodiment, the substrate 2 is a substrate of the LGA (Land GridArray) type and comprises: a core 7; bottom metal regions 8 and topmetal regions 9, for example of copper, which extend on opposite facesof the core 7; and a solder mask 10. A through hole in the substrate 2defines a sound port 11 and enables acoustic coupling of the inside ofthe package structure, in particular of the sensor chip 5, with theexternal environment.

The core 7, which is more clearly visible in FIGS. 29 and 3, is definedby a chip of rigid dielectric material, for example FR4, having alongitudinal dimension and a transverse dimension. In particular, thelongitudinal dimension is greater than the transverse dimension.

The bottom metal regions 8 are arranged on a face of the core 7 facingthe external environment, i.e., opposite to the cap 3. In particular,defined in the bottom metal regions 8 are external contacts 12 forelectrical connection of the microelectromechanical microphone 1 b and,optionally, an external guard ring 13, which surrounds the sound port11. The external guard ring 13 may be used also for connection to groundand is thus also referred to as “ground ring”.

The top metal regions 9 extend on a face of the core 7 facing the sensorchip 5, and are protected by the cap 3. Defined in the top metal regions9 are internal contacts 15, a bonding ring 16, which extends along theperimeter of the core 7, an inner guard ring 17, which surrounds thesound port 11, and a barrier ring 29, which extends over the core 7between the bonding ring 16 and the outer perimeter of the sensor chip5. In greater detail, the barrier ring 29 extends at a distance from thebonding ring 16, thus defining a trench 19 between the barrier ring 29and the bonding ring 16. Through the trench 19 a respective surfaceregion of the core 7 is exposed.

The barrier ring 29 likewise extends at a distance from the outerperimeter of the sensor chip 5, thus defining a further trench 25between the barrier ring 29 and the outer edge of the sensor chip 5. Thetrench 25 has the function of containing a possible excess of glue ofthe bonding layer 23, which could expand laterally to the sensor chip 5during the step of bonding of the sensor chip 5 on the substrate 2. Thedistance between the barrier ring 29 and the sensor chip 5 (i.e., thewidth of the trench 25) is chosen comprised between 50 μm and 100 μm,for example 75 μm. The distance between the barrier ring 29 and thebonding ring 16 (i.e., the width of the trench 19) is chosen comprisedbetween 30 μm and 70 μm, for example 50 μm.

The internal contacts 15 are electrically coupled to respective externalcontacts 12 (belonging to the bottom metal regions 8) through throughvias 20, of metal material, which extend throughout the thickness of thecore 7. In one embodiment, the solder mask 10 is shaped for defining anassembly base for the supporting chip 6 and a contact island 21 thathouses the internal contacts 15. The contact island 21 is formed as arecess in the solder mask 10 so that the internal contacts 15 restdirectly on the core 7 and are in direct connection with the throughvias 20.

The internal contacts 15 are thus separated laterally from the rest ofthe conductive structures present on the face of the substrate 2, thelatter facing the cap 3.

The control chip 6 houses, for example, an ASIC (not illustrated indetail in so far as it is per se known), which comprisessignal-processing circuits (for example, a charge-amplifier circuit fora capacitive electro-acoustic sensor) and the components for interactingwith and enabling operation of the microphone, in particular withregards to transduction of the acoustic signals. According to theembodiment of FIGS. 28-30, the control chip 6 is located between thesensor chip 5 and the contact island 21.

According to a different embodiment (not illustrated), the contactisland 21 extends between the control chip 6 and the sensor chip 5. Thecontrol chip 6 has contact pads 28 for connection to the internalcontacts 15 by first wire bondings 30 and to the sensor chip 5 by secondwire bondings 31.

An electroacoustic transducer 35 is integrated in the sensor chip 5 and,in one embodiment, comprises a membrane 37 of semiconductor material,which extends over a cavity 38 formed in the body 5 a of the sensor chip5, and a rigid metal backplate 40, capacitively coupled to the membrane37. The backplate 40 is provided with holes and is arranged alongsidethe membrane 37 on the side opposite to the cavity 38. The cavity 38 isdelimited on one side by the membrane 37 and faces, on the oppositeside, the sound port 11.

In other words, the sensor chip 5 is coupled to the substrate 2 so thatthe membrane 37 is in acoustic communication with the outside of thepackage structure formed by the substrate 2 and by the cap 3 through thesound port 11. In one embodiment, the sensor chip 5 is centred aroundthe sound port 11.

The sensor chip 5 is coupled to the core 7 of the substrate 2 by abonding layer 23 of glue, in particular, epoxy glue. The bonding layer23 extends between the barrier ring 29 and the inner guard ring 17. Inthis way, the barrier ring 29 prevents contamination of the bonding ring16 by the glue of the bonding layer 23 in so far as it functions asbarrier for the glue. If the glue were to contaminate the bonding ring16, this would jeopardize bonding of the solder paste, thus causingincomplete soldering of the cap 3 or else malfunctioning of themicrophone, up to possible detachment of the cap 3.

The inner guard ring 17 prevents the glue of the bonding layer 23 fromflowing towards, and into, the hole that constitutes the sound port 11.Thus, according to one aspect of the present disclosure, the glue of thebonding layer 23 remains confined between the barrier ring 29 and theinner guard ring 17.

The present applicant has found that thicknesses of the inner guard ring17 that enable the aforesaid purpose to be achieved are comprisedbetween 15 μm and 25 μm, for example 20 μm, with a width, measured inthe direction of the axis X, of at least 30 μm.

The barrier ring 29 has likewise the function of preventing the solderpaste of the solder-paste region 29 from flowing towards the sensor chip5. In fact, if the solder paste were to contaminate the region where thesensor chip 5 and the control chip 6 are positioned, this could cause ashort circuit between the electrical contacts (e.g., bonding wires)present in this region; an excess of solder paste could even extend overthe sensor chip (thus damaging the vibrating membrane) and the controlchip (thus damaging it).

For this purpose, the trench 19 has the function of containing apossible excess of solder paste that might drip from the bonding ring 16towards the inside of the acoustic chamber 4. This possible excess ofsolder paste thus remains trapped within the trench 19, without beingable to flow beyond the barrier ring 29.

The barrier ring 29 has a thickness comprised between 15 μm and 25 μm,for example 20 μm.

An improvement of the performance of the microelectromechanicalmicrophone 1 b may be obtained using sensor chips 5 of larger size,i.e., provided with a more extensive membrane that affords an increasein sensitivity. In this context, the mutual dimensions of all theelements that form the micro-electro-mechanical microphone assume afundamental importance. For instance, the width of the trenches 19 and25 are carefully monitored since, in the event of partial narrowing, therespective trench 19, 25 might no longer be able to contain effectivelythe solder paste 29 and the glue of the bonding layer 23, respectively.In particular, it is to be noted that, for the manufacturing processescommonly used, the normal procedure is to provide the bonding ring 16with some, or all, the corners rounded, as may be seen in the region 33surrounded by a dashed line in FIG. 28. In order to keep a constantdistance between the barrier ring 29 and the bonding ring 16 (so thatthe effect of protection provided by the trench 19 is effective alongthe entire barrier 19), according to one aspect of the presentdisclosure also the barrier ring 29 is made with rounded corners, atleast for the ones that correspond to the rounded corners of the bondingring 16. However, sensor chips 5 of a known type typically have aquadrangular shape with sharp corners 5 a. This causes a reduction ofthe distance between the sensor chip 5 and the barrier ring 29 at thecorners 5 a of the sensor chip 5, where the latter directly face therounded corners of the barrier ring 29; the consequence is a narrowingof the trench 25 at the corners 5 a of the sensor chip 5. A narrowing ofthis type may be such as to jeopardize the capacity of the trench 25 tocontain the glue, which spreads out of the bonding region 23 as a resultof the pressure exerted by the sensor chip 5 during assembly thereof.

In order to overcome this problem, an undesired solution is that ofincreasing further the width of the trench 25, which, however, causes anincrease in the dimensions of the microelectromechanical microphone 1 b.

According to one aspect of the present disclosure amicroelectromechanical microphone 100 b of the type illustrated in FIG.31 is provided. The microelectromechanical microphone 100 b includes asensor chip 105 of a polygonal shape (in this case, quadrangular)defined by faces 105 b radiused to one another by rounded corners 105 a,which have a radius of curvature equal to the radius of curvature thatthe barrier ring 29 presents in corresponding rounded corner regions. Inthis context, the term “rounded corner” indicates a corner that is notsharp, i.e., is defined by a curvilinear radiusing of two faces 105 b ofthe sensor chip 105.

In other words, according to the embodiment of FIG. 31, the outerperimeter of the sensor chip 105 follows, at a definite constantdistance from the trench 25, the inner perimeter of the barrier ring 29.In this way, the trench 25 has a width (defined as distance between apoint of the outer perimeter of the sensor chip 105 and a respectivepoint, aligned along X or along Y, of the inner perimeter of the barrierring 29) that is constant along the entire perimeter of the sensor chip105.

Rounding of the corners 105 a of the sensor chip 105 may be obtained ina per se known manner, for example by laser cutting or plasma cutting.

FIG. 32 shows an embodiment alternative to that of FIG. 31, designed toobtain similar advantages.

Illustrated in FIG. 32 is a microelectromechanical microphone 110 b. Themicroelectromechanical microphone 110 b includes a sensor chip 115 withchamfered corners 115 a. Unlike the embodiment of FIG. 31, in this casethe corners 115 a of the sensor chip 115 are not rounded, but cut, forexample by laser cutting or plasma cutting. Thus, after cutting, thecorners 115 a have a chamfered region that is substantially planar andnot rounded, as in the embodiment of FIG. 31.

In the context of the present disclosure, the term “chamfered corner”indicates a corner that is not sharp, but cut, i.e., having a planarradiusing between two adjacent faces 115 b.

Chamfering of the corners is performed so that, at the end of themachining steps, the trench 25 has a width, at the chamfered corners 115a, that is the same as or greater than the width along the lateral faces115 b of the sensor chip 115.

FIG. 33 shows a further embodiment of the present disclosure. In thiscase, a microelectromechanical microphone 120 b has a sensor chip 125 inwhich only a portion 125 a of the corners is chamfered, or cut, inparticular a bottom portion that extends along Z starting from thesubstrate 2 (i.e., from the bottom face of the sensor chip 125) and doesnot reach the top face of the sensor chip 125. For instance, the cut ismade for half the extension of the corners so that the bottom half has achamfered, or generically cut, region 125 a, and the top half does notpresent any difference with respect to the case of FIG. 30 (the top halfis a sharp corner). Cutting, or chamfering, is carried out at thecorners of the sensor chip 125. The characteristics of the partial cutare similar to those already described with reference to FIG. 32.

FIG. 34 shows a further embodiment of the present disclosure. In thiscase, a microelectromechanical microphone 130 b has a sensor chip 135 inwhich only a portion of the edges 135 a is chamfered, or cut, inparticular a bottom portion, as in the case of FIG. 34. However, in thisembodiment, the sensor chip 135 is further machined for removingperimetral portions of the sensor chip 135 also on the lateral faces 135b, and not only on the corners 135 a. There is thus formed a lateraletch 136 that extends along the entire perimeter of the sensor chip 135starting from the bottom face, which is coupled to the substrate 2 ofthe sensor chip 135, but without reaching the top face of the sensorchip 135. In this way, the area of the bottom face of the sensor chip135 is smaller than the area of the top face thereof. The sensor chip135 is thus mushroom-shaped, where the top face of the sensor chip 135has an area greater than that of the bottom face of the sensor chip 135.In particular, the area of the top face is 5%-25% greater than the areaof the bottom face; more in particular, it is 15% greater than the areaof the bottom face.

Chamfering of the entire perimeter of the sensor chip 135 is performedin the bottom half of the sensor chip 135, i.e., in the portion of thesensor chip 135 that is in contact with the substrate 2, in order not toreduce or damage the top portion of the chip 135 that houses themembrane. In this way, it is possible to use a sensor chip 135 having awide sensitive area (membrane), but having a base for bonding with thesubstrate 2 of smaller size and in any case such as not to reduce thewidth of the trench 25 beyond a minimum value fixed in the design stage.

FIG. 35 is a lateral sectional view of the microelectromechanicalmicrophone 130 b of FIG. 34. As may be noted from FIG. 35, the lateraletch 136 of the sensor chip 135 extends, along Z, for a height greaterthan the thickness, once again along Z, of the barrier ring 29. In thisway, the lateral portions of the sensor chip 135 outside the etch 136may extend over the trench 25 (covering it at the top) and possibly alsoover the barrier ring 29, without affecting the capacity of the trench25 to withhold adequately any glue that might come out of the bondingregion 23.

Manufacture of the microelectromechanical microphone 1 b of FIGS. 28-30,as of the microelectromechanical microphones 100 b, 110 b, 120 b and 130b according to the respective embodiments, may be carried out in the waydescribed hereinafter. Initially, the outer metal layer 8, the innermetal layer 9, and the solder mask 10 are defined with photolithographicprocesses to obtain the external contacts 12, the internal contacts 15,the bonding ring 16, the inner guard ring 17, and the barrier ring 29.Then, the bonding layer 23 is formed by dispensing glue between theinner guard ring 17 and the barrier ring 29, in the region in which itis desired to arrange the sensor chip 5. A bonding layer (notillustrated) is provided on the solder mask 10, in the region where itis desired to position the control chip 6. The latter is then bonded tothe solder mask 10 by the bonding layer. Also the sensor chip 5 isjoined to the substrate 2 in the glue layer previously dispensed.Finally, the wire bondings 30 are provided between the control chip 6and the internal electrodes 15, and the wire bondings 31 are providedbetween the control chip 6 and the sensor chip 5. The cap 3 is thenjoined to the bonding ring 16 of the substrate 2 to obtain the structureof FIG. 28 or of FIGS. 31-34, according to the respective embodiments.According to the embodiments of FIGS. 31-34, the sensor chip 5 ismachined prior to the step of bonding with the substrate 2. As mentionedpreviously, it is possible to shape the sensor chip 5 by laser cuttingor plasma cutting, or else by steps, in themselves known, of lithographyand selective chemical etching.

FIG. 36 illustrates an electronic system 200, which incorporates any ofthe microelectromechanical microphones described herein, such asmicroelectromechanical microphones 1, 1 a, 1 b, 100, 100 a, and 100 b,110 b, 120 b, and 130 b, but is shown and described with reference tomicroelectromechanical microphone 1.

The electronic system 200 may be an electronic device of any type, inparticular a portable device supplied autonomously, such as, by way ofnon-limiting example, a cellphone, a portable computer, a video camera,a wearable device, such as a watch, a photographic camera, a multimediareader, a portable apparatus for videogames, a motion-activated userinterface for computers or consoles for videogames, asatellite-navigation device, etc. In the embodiment of FIG. 36, theelectronic system 200 is a cellphone.

A microelectromechanical microphone 1, which may be any of themicroelectromechanical microphones described herein, such asmicroelectromechanical microphone 1, 1 a, 1 b, 100, 100 a, 100 b, 110 b,120 b, and 130 b, and may be coupled to an acquisition interface 202 ofan audio module 201. The electronic system 200 may further comprise acasing 203, rigidly coupled to which is an impact sensor 204, a controlunit 205, a memory module 206, an RF communication module 207 coupled toan antenna 208, a display 210, a filming device 212, a serial-connectionport 213, for example a USB port, and a battery 215 for autonomoussupply.

The control unit 205 co-operates with the microelectromechanicalmicrophone 1, for example exchanging signals through the audio module201.

It should be noted that the scope of the present disclosure is notlimited to embodiments having necessarily specifically one of thedevices listed or all of them together.

The present applicant has found that, given the same dimensions, it ispossible to obtain an improvement in the performance as compared tomicroelectromechanical microphones of a known type, or, alternatively,obtain the same performance as that of microelectromechanicalmicrophones of a known type but in a smaller package. For instance, byshaping the sensor chip 5 as described and illustrated in FIGS. 31 to35, it is possible to increase the sensitive area (i.e., the area of thesensor chip 5 containing the membrane) by approximately 25% with respectto known solutions, without increasing the overall dimensions of theelectromechanical microphone thus obtained. Finally, it is evident thatmodifications and variations may be made to the microelectromechanicalmicrophone described herein, without thereby departing from the scope ofthe present disclosure.

For instance, according to a variant that may be applied to some of theembodiments described, such as FIGS. 28-35, the barrier ring 29 isU-shaped and extends for surrounding the sensor chip on three sides,except for the side of the sensor chip directly facing the solder mask10. A possible spreading of the glue of the bonding region 23 towardsthe solder mask 10 does not jeopardize the performance of themicro-electro-mechanical microphone. In this case, etching 136 of theembodiment of FIGS. 34 and 35 may extend to just three sides of thesensor chip 135 (i.e., the etch 136 is U-shaped), i.e., the etch 136extends into the sides of the sensor chip 135 directly facing theU-shaped barrier, and does not directly face the solder mask 10 at theside of the sensor chip 135.

In various embodiments, sound port may be provided in the cap instead ofin the substrate, which may thus be continuous in a region correspondingto the sensor chip. Similarly, it is possible to use substrates both ofthe LGA type and of the BGA type for electrical connection towards theoutside.

The various embodiments described above can be combined to providefurther embodiments. These and other changes can be made to theembodiments in light of the above-detailed description. In general, inthe following claims, the terms used should not be construed to limitthe claims to the specific embodiments disclosed in the specificationand the claims, but should be construed to include all possibleembodiments along with the full scope of equivalents to which suchclaims are entitled. Accordingly, the claims are not limited by thedisclosure.

1. A microelectromechanical microphone comprising: a supportingsubstrate having a first face, a second face, and a through openingextending from the first face to the second face; a sensor chip bondedto the first face of the supporting substrate and integrating amicroelectromechanical electroacoustic transducer; and a control chip inthe through opening and extending at least from the first face of thesupporting substrate to at least the second face of the supportingsubstrate, the control chip being operatively coupled to the sensorchip, the sensor chip being at least partially arranged on a surface ofthe control chip.
 2. The microelectromechanical microphone according toclaim 1, wherein the supporting substrate has a through hole between thefirst face and the second face, and the control chip is housed in thethrough hole.
 3. The microelectromechanical microphone according toclaim 2, comprising a fixing structure laterally surrounding the controlchip, wherein the control chip is coupled to the supporting substrate bythe fixing structure.
 4. The microelectromechanical microphone accordingto claim 1, wherein the sensor chip is at least partially bonded to thesurface of the control chip.
 5. The microelectromechanical microphoneaccording to claim 1, wherein the control chip extends beyond the firstface of the supporting substrate.
 6. The microelectromechanicalmicrophone according to claim 5, wherein the control chip includes arecess that receives a portion of the sensor chip.
 7. Themicroelectromechanical microphone according to claim 6, wherein thecontrol chip extends beyond the second face of the supporting substrate.8. The microelectromechanical microphone according to claim 1, whereinthe control chip has a first thickness and the supporting substrate hasa second thickness, the second thickness being less than firstthickness.
 9. A microelectromechanical microphone comprising: asupporting substrate having a first face, a second face, and a throughopening extending from the first face to the second face; a control chipin the through opening, a first surface of the control chip extendingbeyond the first face of the supporting substrate; and a sensor chipcoupled to the first face of the supporting substrate, the sensor chipintegrating a microelectromechanical electroacoustic transducer, thesensor chip being operatively coupled to the control chip and at leastpartially arranged on a surface of the control chip.
 10. Themicroelectromechanical microphone according to claim 9, wherein a secondsurface of the control chip extends beyond the second face of thesupporting substrate.
 11. The microelectromechanical microphoneaccording to claim 9, comprising a base coupled between the sensor chipand the supporting substrate.
 12. The microelectromechanical microphoneaccording to claim 11, wherein a surface of the base is coplanar withthe first surface of the supporting substrate.
 13. Themicroelectromechanical microphone according to claim 9, wherein thecontrol chip includes a recess that receives a portion of the sensorchip.
 14. A microelectromechanical microphone comprising: a supportingsubstrate having a first face, a second face, and a through opening; acontrol chip in the through opening and having a first surface thatextends beyond the first face of the supporting substrate and a secondsurface that extends beyond a portion of the second face of thesupporting substrate; and a sensor chip coupled to the first face of thesupporting substrate, the sensor chip integrating amicroelectromechanical electroacoustic transducer, the sensor chip beingoperatively coupled to the control chip and a portion of the sensor chipbeing directly coupled to a surface of the control chip.
 15. Themicroelectromechanical microphone according to claim 14, wherein thethrough opening in the supporting substrate being a first throughopening, the supporting substrate including a second through opening,wherein the sensor chip is coupled to the first face of the supportingsubstrate at the second through opening.
 16. The microelectromechanicalmicrophone according to claim 14, comprising a base coupled between thesensor chip and the supporting substrate.
 17. The microelectromechanicalmicrophone according to claim 16, wherein a surface of the base iscoplanar with a surface of the supporting substrate.
 18. Themicroelectromechanical microphone according to claim 14, comprising acap coupled to the supporting substrate, wherein the cap include athrough opening.
 19. The microelectromechanical microphone according toclaim 14, wherein the control chip includes a plurality of conductivethrough vias.
 20. The microelectromechanical microphone according toclaim 14, wherein the control chip is fixed to walls of the supportingsubstrate in the through opening by polymeric material.